自定义头文件和包含库[C ++]

Question

If I create a header like this:

#ifndef _MY_HEADER_H
#define _MY_HEADER_H

#include <iostream>
void foo();

#endif

With it's correspondent .cpp file, do I need to include iostream in the main.cpp file?

Answer 1

不必在main.cpp版本中再次包含它，就像在main.cpp版本中那样，如果您包含相同的.h版本，则包含的内容将自动在编译中可用，为什么还要编写额外的冗余行？

Answer 2

To answer you question: No you don't need to include it (again).

But it is good practice, to include in the header only the stuff that is required for the header to work. So if your foo() method requires iostream , you should include it. If you create a class that uses only pointers or references to other classes you should prefer forward declarations over inclusion of the full-fledged header of the respective classes.